This is a resubmission application of our research proposal (1 R01 HL089504-01), entitled: Plaque Inflammation and Dysfunctional HDL in AIM-HIGH. The overall goal of this proposal is to use state-of-the-art imaging and proteomic approaches to understand the roles of macrophages and HDL in preventing CHD in a subset of the unique participants available from the AIM-HIGH Trial. By utilizing the well-established AIM HIGH trial recruitment, clinical site and data collection infrastructure, this Substudy will be much more efficient and cost-effective than would a stand-alone, multi-center trial. In preliminary studies, we have found a strong correlation between a dynamic contrast enhanced (DCE-MRI) parameter, Ktrans, and plaque inflammation, and also have obtained preliminary evidence that CHD is characterized by oxidative and inflammatory changes in HDL that are associated with impairment of its normal function but that are improved with statin+niacin therapy. In this context, the AIM-HIGH cohort represents a unique opportunity to investigate the relative effects of simvastatin or simvastatin+niacin on specific inflammatory changes in atherosclerotic plaques. Based on these findings, we propose a Substudy that will enroll 120 participants (60 per treatment group) from Dr. Xue-Qiao Zhao's Substudy of MR imaging in AIM-HIGH patients. We will perform post processing of MR images to derive parameters associated with carotid inflammation and measure plasma HDL oxidation and protein composition at baseline and after 2 years on either simvastatin or simvastatin+ niacin. In Aim 1, we will test the hypothesis that simvastatin+niacin results in greater reduction in the carotid inflammation marker, Ktrans, at 2 years than does simvastatin alone. In Aim 2, we will test the hypothesis that 2 years of simvastatin+niacin results in greater reduction in HDL oxidation and normalization of HDL protein composition than does simvastatin alone. In Aim 3, we will test the hypothesis that HDL oxidation changes over 2 years correlate better with reduction in Ktrans than do changes in HDL levels alone. Thus, this Substudy will use novel, state-of-the-art, non-invasive imaging and protein analytical tools to determine whether niacin therapy in concert with a statin reduces plaque inflammation and dysfunctional HDL to a greater extent than does a statin alone. The results would provide strong support for the hypothesis that niacin-induced alterations in HDL are of central importance in decreasing atherosclerotic plaque inflammation. Despite the development of lipid-lowering drugs like statins, coronary heart disease (CHD) remains the leading cause of death in the U.S. CHD events occur when inflammation breaks down the structure of atherosclerotic plaques. Adding niacin to statins might help stabilize plaques, but we don't know exactly how niacin might work to do this. We will test the hypothesis that niacin helps to block the inflammation that breaks down atherosclerotic plaques by improving the ability of good cholesterol, HDL, to repair inflammatory damage to the plaque.